What is Chapter 04 of ICD-11?
The Chapter 04 gathers the diseases of the immune system. In ICD-10, these disorders were included in chapter III along with diseases of the blood and hematopoietic organs. In ICD-11, its own chapter was created to better reflect the complexity of immune processes.
The official guide notes that this new chapter was designed to better capture the disease processes of the immune system and that, in general, more details were added to the chapter, including specific sections for autoinflammatory disorders and allergic or hypersensitivity conditions.
Structure of chapter 04
According to the WHO Reference Guide, chapter 04 has the following main sections:
- Immunodeficiencies
- Specific non-organic systemic disorders
- Autoinflammatory disorders
- Allergic or hypersensitivity conditions
- Certain diseases that affect the immune system
- Thymus diseases
The WHO also summarizes the main hierarchy of the chapter as follows:
| Grouping | Summary hierarchy |
|---|---|
| Immunodeficiencies and specific non-organic systemic disorders | 1st level: main grouping 2nd level: broad disease category/type of disorder 3rd level: specific disease 4th level: greater specificity |
| Autoinflammatory disorders | 1st level: autoinflammatory disorders 2nd level: specific syndrome |
| Allergic or hypersensitivity conditions | 1st level: allergic or hypersensitivity condition · 2nd level: broad category by body systems |
| Certain diseases that affect the immune system | 1st level: main grouping 2nd level: specific disease 3rd level: greater specificity |
| Thymus diseases | 1st level: thymus diseases · 2nd level: specific disease/type of disorder |
Big blocks of Chapter 04
Click on each block to see a brief explanation of how the section is organized within ICD-11.
The first major grouping of the chapter includes the immunodeficiencies. In the official comparison with ICD-10, the WHO specifically highlights the primary immunodeficiencies and the acquired immunodeficiencies as part of the new structure of chapter 04.
The guide includes this grouping as one of the main sections of chapter 04. Its organization follows the logic of broad categories and then specific diseases or types of disorder, with an additional level of greater specificity.
The WHO highlights the autoinflammatory disorders as its own section of chapter 04. This shows the increase in detail of ICD-11 compared to ICD-10 in the immune field.
In this section, the hierarchy is simpler: first the group of autoinflammatory disorders and then the specific syndrome.
One of the most visible new features of chapter 04 is the inclusion of a specific section for allergic or hypersensitivity conditions. The guide itself expressly mentions it as an important expansion with respect to the ICD-10.
The hierarchy of this section starts from the allergic or hypersensitivity condition and then organizes the groups by body systems.
Official comparison with ICD-10 shows that chapter 04 includes a grouping for certain disorders or diseases that affect the immune system, with greater detail than in the previous classification.
| Examples visible in the guide | Observation |
|---|---|
| Immune system disorders affecting white cell lineages | It appears as a specific grouping of chapter 04. |
| Certain immune system disorders | They are mentioned as a distinct category within the new chapter. |
The guide also includes a section for thymus diseases, with a hierarchy based on the specific disease or type of disorder.
Comparison ICD-10 vs ICD-11 — Chapter 04
The WHO summarizes the transition from the previous structure to the new one:
| ICD-10 block | Equivalent structure of ICD-11 |
|---|---|
| D80–D89 Certain disorders affecting the immune mechanism | Primary immunodeficiencies |
| D80–D89 Certain disorders affecting the immune mechanism | Acquired immunodeficiencies |
| D80–D89 Certain disorders affecting the immune mechanism | Autoinflammatory disorders |
| D80–D89 Certain disorders affecting the immune mechanism | Allergic or hypersensitivity conditions |
| D80–D89 Certain disorders affecting the immune mechanism | Immune system disorders affecting white cell lineages |
| D80–D89 Certain disorders affecting the immune mechanism | Certain immune system disorders |
| D80–D89 Certain disorders affecting the immune mechanism | Thymus diseases |
Reading and coding guidance
1. Separate immunity from hematology
The first rule of thumb is not to continue reading these disorders as if they were still within the old ICD-10 Chapter III. In ICD-11, immune disorders have their own chapter.
2. Identify the main clinical syndrome
The guide explains that the immune system is mainly classified by clinical syndrome. That is one of the keys to correctly navigate chapter 04.
3. Check if the condition is allergic, autoinflammatory or immunodeficiency
The new structure forces us to better distinguish the type of immune process: immunodeficiency, autoinflammation, allergy or hypersensitivity, alterations linked to white cell lineages or thymus diseases.